The invention relates to a method of manufacturing a rigid electrical pin insulator for supporting an electrical conductor, the insulator comprising an electrically insulating rigid core obtained by molding and having a top end, a bottom end with a bore for receiving said pin and extending in an axial direction between said top and bottom ends, and an outer surface covered in a dielectric covering obtained by molding and having a shaped outside surface defining at least one groove for supporting said electrical conductor and having fins that are annular about the axis of the bore.
Such an insulator is generally designed to be installed on a high voltage or medium voltage electricity pylon, e.g. to support an electrical conductor such as an optionally insulated cable of an electricity transport line, while keeping the cable electrically insulated from the pylon.
Thus, such an insulator is generally subjected to high mechanical stresses due in particular to the weight of the cable it supports, while also providing a high degree of electrical insulation. Conventionally, such an insulator has been made of glass or porcelain, and recent developments in materials have led to this type of insulator being made, for example, out of composite material, thereby saving a considerable amount of weight compared with glass and also reducing manufacturing costs, but presenting difficulties associated with molding such composite materials.
One such composite material insulator is known from U.S. Pat. No. 5,945,636. In that known insulator, the core, which is covered in a thin skin for protecting the core from environmental attack, is itself solid and of varying thicknesses, thus making it difficult to mold without any internal defects.
In general, when a solid piece is obtained by molding, there is a danger of shrink cavities arising or indeed of residual stresses remaining due in particular to the material shrinking as it cools. Thus, when a solid part is to be molded, one of the difficulties lies in implementing a molding technique that is adapted to avoiding such irregularities.
For example, in order to mold a solid piece, it is possible to add vents and feeders for facilitating the flow of material in the mold and for ensuring that pressure is uniform in the cast piece so as to avoid giving rise to mechanical irregularities such as holes or shrink cavities. The drawback of such solutions is that they complicate the shape of the mold, they increase manufacturing cycle time, and they need to be developed empirically, which constitutes an overhead cost in manufacture.
The object of the invention is to remedy those drawbacks.
To this end, the invention provides a method of manufacturing a rigid electrical pin insulator for supporting an electrical conductor, the insulator comprising an electrically insulating rigid core obtained by molding and having a top end, a bottom end with a bore for receiving said pin and extending in an axial direction between said top and bottom ends, and an outer surface covered in a dielectric covering obtained by molding and having a shaped outside surface defining at least one groove for supporting said electrical conductor and having fins that are annular about the axis of the bore, wherein said core is molded in such a manner that its outside surface defines radial ribs which extend in the axial direction from the top end of the core, said ribs being spaced apart from one another by a distance that is constant and substantially equal to the thickness of the core.
Such a method simplifies the manufacture of a pin insulator by molding a composite material by avoiding problems associated with molding parts of excessive thickness while not harming the mechanical and electrical properties of the insulator and not increasing the cost of manufacturing the insulator.
In a particular implementation of the method of the invention in which the core and said dielectric covering are molded out of the same material, the covering being overmolded onto said core, good cohesion is obtained between the core and the covering.
In another particular implementation of the method of the invention, in which the core and said dielectric covering are molded out of different materials, the covering being engaged on said core, it is possible to select the materials so as to best optimize manufacturing cost of the insulator as a function of the desired mechanical and electrical performance.
In yet another particular implementation of the method of the invention, in which the core is made of epoxy, and/or silicone, and/or thermoplastic materials, and/or polyester, and/or composite material, a low cost insulator is obtained.
In yet another particular implementation of the method of the invention in which the core is built up from a plurality of molded parts, each of which is of substantially constant thickness, it is possible to obtain a solid insulator of large dimensions.